The present invention relates to a reagent composition for measuring hydrogen sulfide and a method for measuring hydrogen sulfide by using the reagent composition, which reagent composition comprising a specific aniline derivative and an oxidizing agent.
Hydrogen sulfide is colorless gas with a rancid smell which occurs naturally in volcanic gases, mineral springs, etc. and is also produced from rotten sulfur-containing proteins. Hydrogen sulfide is industrially present in exhaust gas and waste liquid from factories, etc. Hydrogen sulfide released in the air can sometimes be oxidized to sulfurous acid gas. Hydrogen sulfide and sulfurous acid gas are harmful to a human body. Sulfurous acid gas is a cause of acid rain and is problematical for the environment. The concentrations of these gases are therefore regulated. From this viewpoint, it is beneficial to healthy life to measure the hydrogen sulfide concentration in the air, rivers, soil, and exhaust gas or waste liquid from factories.
As described above, measurement of hydrogen sulfide is environmentally useful and various methods have been used for determining the hydrogen sulfide concentration. For example, methods using a lead acetate paper strip or a lead acetate detector tube and colorimetric methods, such as iodometry and a Methylene Blue method, (see Talenta, No. 4, p. 227 (1960)) are known.
However, the conventional methods for measuring hydrogen sulfide in the air, exhaust gas, or waste liquid require a large quantity of a sample due to insufficient detection sensitivity, which makes the sampling operation troublesome. Accordingly, an object of the present invention is to provide a method for measuring hydrogen sulfide which are simpler and yet more sensitive than conventional methods or determining hydrogen sulfide.
As a result of extensive studies, the inventor of the present invention found that hydrogen sulfide concentration can be determined simply and with high sensitivity by using the aniline derivative represented by the general formula (I), resulting in accomplishment of the present invention.
Thus, the present invention provides a reagent composition for measuring hydrogen sulfide, which comprises an aniline derivative represented by the general formula (I): 
wherein R1 and R2 independently represent a substituted or unsubstituted C2-C6 alkyl group, and R3 and R4 independently represent a hydrogen atom, a C1-C6 alkyl group or a halogen atom; and an oxidizing agent.
The present invention also provides a method for measuring hydrogen sulfide, which can be considered as an improved Methylene Blue method, which comprises reacting the aniline derivative represented by the general formula (I) above and an oxidizing agent with hydrogen sulfide in a solution under an acidic condition, and colorimetrically analyzing the resulting solution.